Structural studies of bis(histidinato)nickel(II): Combined experimental and computational studies

A distorted octahedral nickel(II) complex, Ni(2-amino-3-(1H-imidazol-4-yl)propanoic acid)₂] (1), has been synthesized by a solvothermal method and characterized by single-crystal X-ray diffraction. Geometry optimization in the gas phase and pyridine together with Hirshfeld surface and reduced density gradient analyses reveal that this complex shows different distortions from octahedral in the gas, liquid, and solid phases. The reason seems to be because of the presence of two intramolecular NH⋯O weak interactions in the gas phase and two sets of rather strong intermolecular NH⋯O and CH⋯O interactions in the solid phase. Time-dependent density functional theory (TD-DFT) calculations suggest that these different distortions result in different electronic absorption spectra.